The overall goal of this proposal is to evaluate the safety and therapeutic potential of in vivo blockade of the PD-1 (Programmed death-1) co-inhibitory pathway to achieve a functional cure (long-term control in the absence of antiretroviral therapy) for HIV/AIDS using the SIV/macaque model. Dysfunctional anti- HIV immunity and persistence of viral reservoirs represent the two major issues that must be addressed by therapeutic approaches targeting functional cure. We believe that these two issues can be addressed effectively by targeting the PD-1 co-inhibitory pathway d uring ART. Our recent studies have demonstrated that PD-1 blockade synergizes with ART to enhance control of viral rebound following ART interruption up to 6-80 fold. We think these results are remarkable since this was observed in animals that were subjected to ART at 30 weeks after SIV infection by which time the damage to the host immune system was severe and virus would have accumulated many escape mutations. Multiple studies including our own have demonstrated that viral reservoirs are concentrated in GC-Tfh during ART and it is critical to generate anti-viral CD8 T cells with homing potential to GC. However, the dogma until recently has been that anti-viral CD8 T cells do not home to GC. However, others and we recently defined a novel subset of CXCR5+ CD8 T cells with potential to home to GC (Follicular CD8) and contribute to control of SIV. Importantly, we now know that CD40L-adjuvanted DNA/MVA vaccine can induce CXCR5+ CD8 T cells in SIV uninfected rhesus macaques. The ongoing studies are addressing the efficacy of combining PD- 1 blockade with therapeutic vaccination using CD40L and TLR7/8 agonist as adjuvants. Based on these results we propose the following 3 focus areas for the next 5 years of this R37: Area 1 ? Synergy between PD-1 blockade, therapeutic vaccination and other immunotherapies. Area 2 ? Optimizing conditions to improve generation of follicular homing CD8 T cells. Area 3 ? Targeting the PD-1 blockade to SIV-infected cells. By completion of these studies, we hope to develop an effective immunotherapy to achieve functional cure for HIV/AIDS. RELEVANCE (See instructions): WHO estimates that there are currently 32 Million humans living with HIV/AIDS. There is a great need for developing therapeutic approached that achieve functional cure (long term control of HIV in the absence of combination antiretroviral therapy). The goal of this grant is to identify a functional cure for HIV by targeting PD-1 inhibitory pathway using anti-PD-1 antibody combined with ART and vaccination.